The Life Sciences Recent Progress and Application to Human Affairs The World of Biological Research Requirements for the Future (1970) / Chapter Skim
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Development of an Organism
Development of an Organism
Pages 71-79
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From page 71... ...
The free-livine mammalian cell is motile and proceeds ~ ;, ~ through round alter round ot the cell cycle, out wnen cells In culture nnc~ each other and establish physical contact, motility abruptly ceases and the cells are likely to remain in phase Go. Whatever may initiate the cancerous transformation, the consequences are exactly the reverse, regaining of motility and re-entry into Stage S
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From page 72... ...
Tiny embryo sections taken from an area that, from past experience, should go on to become working muscle have been grown in tissue culture; they go through repeated cell divisions, and, at a characteristic time, the cells gather together to form a primitive "myotube." Cell membranes become obscure as the cells blend into a single syncytium, which then begins to contract spontaneously. But the initial cell samples were found to have contained two types of cells: One type normally goes on to become muscle, and one becomes the fibroblasts responsible for the synthesis of the connective tissue protein, collagen, as well as the variety of carbohydrate polymers that are secreted into the medium.
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From page 73... ...
What chemical attraction leads the growing nerve cell to the portion of the retina to which it was "foreordained"? If man is to understand himself, to find new bases for contraceptive techniques, to find diagnostic procedures that can detect improperly fashioned fetuses early in pregnancy, perhaps one day to undertake surgical repair of such fetuses, it is imperative that an intensive effort be made to understand the fundamentals of the process of differentiation.
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From page 74... ...
Upon the approach of the sperm, its "acrosome," the bulge at the leading edge, burrows through the egg cell membrane, the sperm nucleus seeks and finds the egg cell nucleus, and these fuse. Shortly thereafter, the ribosomes become "activated," the nucleoli begin to disappear, more ribosomes appear in their stead, and the preformed messages begin to be read.
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From page 75... ...
Closely timed and precisely interlocking, these events produce all the major features that finally characterize the adult nervous system-e.g., a recognizable neural axis with appropriately segregated parts, rudiments of cranial and spinal nerves, and enlargements, foldings, and outpocketings that foretell both the final gross form and the inner detail of localized cell groupings. The key point is that the final unity emerges from the coordinated activity of thousands of individual cells, each engaging in one or more of the four activities mentioned, each behaving as if it knew its place in the final structure, yet each subordinating itself to that structure.
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From page 76... ...
For example, in the cocklebur, a common weed that will never flower if kept under continuous light, flowering will be initiated if the plant is exposed only once to a dark period more than nine hours long, even if it is immediately replaced in continuous light. No anatomical or biochemical test has yet distinguished between induced and noninduced plants immediately after the inducing dark period.
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From page 77... ...
Understanding of the cancer cell and the neoplastic process in molecular terms, a hopeless pursuit several years ago, is now a realistic research goal for those studying tumorigenic viruses and the mechanism of virus-induced cell transformation. Because tumor-producing viruses can now be obtained in highly purified form and suitable "normal" cells in culture can be transformed into "neoplastic" cells, experimental systems are becoming available for a rational analysis of the molecular basis of neoplasia.
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From page 78... ...
By infecting homogeneous cell cultures, one can insert viral genetic material of different types and sizes into defined intracellular regions and study the ensuing biosynthetic events. Studies with representative members of the four DNA virus groups, during the past five years, have revealed the following series of events during an infectious cycle: (1)
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From page 79... ...
distinct from virion structural proteins argues for the persistence and functioning of at least part of the viral genome in the tumor cell. The direct demonstration of viral DNA in virus-induced tumor cells is a technically formidable problem since a single viral gene would represent a very small portion of total cellular DNA, about one part in a million.
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